Publications

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Vertical wafer stacking will enable a wide variety of new system architectures by enabling the integration of dissimilar technologies in one small form factor package. With this LDRD, we explored the combination of processes and integration techniques required to achieve stacking of three or more layers. The specific topics that we investigated include design and layout of a reticle set for use as a process development vehicle, through silicon via formation, bonding media, wafer thinning, dielectric deposition for via isolation on the wafer backside, and pad formation.

Results of several experiments aimed at remedying photoresist adhesion failure during spray wet chemical etching of InGaP/GaAs NPN HBTs are reported. Several factors were identified that could influence adhesion and a Design of Experiment (DOE) approach was used to study the effects and interactions of selected factors. The most significant adhesion improvement identified is the incorporation of a native oxide etch immediately prior to the photoresist coat. In addition to improving adhesion, this pre-coat treatment also alters the wet etch profile of (100) GaAs so that the reaction limited etch is more isotropic compared to wafers without surface treatment; the profiles have a positive taper in both the [011] and [011] directions, but the taper angles are not identical. The altered profiles have allowed us to predictably yield fully probe-able HBTs with 5 x 5 {micro}m emitters using 5200 {angstrom} evaporated metal without planarization.

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This paper summarizes an evaluation of a treatment loop designed to upgrade the quality of spent rinse waters discharged from 10 wet benches located in the fab at Sandia's Microelectronics Development Laboratory (MDL). The goal of the treatment loop is to make these waters, presently being discharged to the fab's acid waste neutralization (AWN) station, suitable for recycling as feed water back into the fab's ultrapure water (UPW) plant. The MDL typically operates 2 shifts per day, 5 days per week. Without any treatment, the properties of the spent rinse waters now being collected have been shown to be compatible with recycling about 30% (50/168) of the time (weekends primarily, when the fab is idling) which corresponds to about 12% of the present water discharged from the fab to the AWN. The primary goal of adding a treatment loop is to increase the percentage of recyclable water from these 10 wet benches to near 100%, increasing the percentage of total recyclable water to near 40% of the total present fab discharge to the AWN. A second goal is to demonstrate compatibility with recycling this treated spent rinse water to the present R/O product water tank, reducing both the present volume of R/O reject water and the present load on the R/O. The approach taken to demonstrate achieving these goals is to compare all the common metrics of water quality for the treated spent rinse waters with those of the present R/O product water. Showing that the treated rinse water is equal or superior in quality to the water presently stored in the R/O tank by every metric all the time is assumed to be sufficient argument for proceeding with plans to incorporate recycling of these spent rinse waters back into MDL's R/O tank.